THE AUTOMOBILE 279 



gas is not available, hydrogen gas may be generated by using 

 zinc and hydrochloric acid. 



2. To show that this explosion has the power to do work. Cut 

 a hole in the side of a coffee pot near the bottom big enough 

 to admit the end of a Bunsen burner. Halfway up on the 

 side make a small hole. Turn on the gas and bring a lighted 

 match near the small hole. Why does the cover fly back? 

 Close the cover and see how many times it can be made to fly 

 back. Turn off the gas and clean out the products of combus- 

 tion from the pot. Then try the experiment again. What 

 do the results show ? 



3. To show how the gas is ignited. Set up an induction coil 

 and cells and show the formation of the spark. 



4. Run a small gas engine with illuminating gas. Notice 

 carefully how each part works. Or make a study of a model. 

 Make a drawing and explain the use of the various parts. 



Other devices. Clutch. The clutch is a device by means 

 of which the engine may be allowed to run alone without 

 moving the wheels of the automobile. This serves two pur- 

 poses. When starting the car, it is necessary to allow the 

 engine to get full speed before putting on the load; then 

 after the engine is once started, the clutch may be gradually 

 thrown in and the car starts. And again, when it is desired 

 to stop for a very short time, the clutch may be thrown out 

 and the engine need not be stopped ; this saves starting the 

 engine again. The most common kind of clutch is the 

 friction type, in which the parts are held so closely together 

 by springs that they rotate together. The tension of the 

 springs is released by means of a foot pedal, thus allowing the 

 parts to operate separately. 



Gear box. The gear box is a mechanism by means of 

 which the speed and driving power of the engine may be 

 changed. These are spoken of as the high and low gear. 

 When climbing a hill, it is desirable to increase the power 

 and lessen the speed. The gear box contains different 



